torbjorn |
Posted: Mon Jul 30, 2007 12:12 pm Post subject: |
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Begin with trying alternatively CVBS (composite) and RGB signal from your digital sources and check if the you have the sync problem in both cases.
In some cases, TVs have badly designed input stages for the video signal which cause clipping of the sync pulses if the signal source has a DC offset that the TV manufacturer did not cater for. In order to assess a such problem properly, one must study the circuit diagram for those parts of the TV, measure the incoming video signal by oscilloscope and check DC offsets etc, and possibly make some kind of test hookup to change the DC offset of the signal.
I have once tried using a bench power supply connected in series with a 1 kohm 2 W resistor in parallell to the video signal, then it is easy to change the DC offset by adjusting the output voltage and polarity of the power supply.
According to official standards for video signals, the black level should be at 0 V, sync tips at approximately -0,3 V and white level at +0,7 V. But in order to save a negative supply voltage, much consumer electronics have sync tips at 0 V, black level +0,3 V and white level +1,0 V. In really weird cases, several volts of positive offset have been found. |
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